Continuous particle number size distribution measurements (5-600nm diameter) were conducted at a tall building site (260m AGL) near downtown Houston and on-board the DOE G-1 aircraft during the TEXAQS-2000 study between August 21 and September 13. Measurements at the building site showed that on about one-half of the days, results demonstrate recent aerosol formation near the sampling site and that freshly formed particles grew from the nucleation to Aitken mode.

Particle formation events demonstrated a distinct diurnal trend with starting times associated with the rapid growth of the convective boundary layer, typically between 9 and 10am in the morning. Newly formed particles appeared at the tall building site after the top of the developing boundary layer lifted above the measurement altitude. During the following 2-5 hours freshly nucleated particles were observed to grow by condensation into the 40-100 nm diameter size range. The observed nucleation mode growth had only a minor effect on ambient aerosol mass concentrations, but Aitken mode number concentrations typically increased by one order of magnitude during the nucleation events.

The coincidence of particle nucleation and boundary layer growth times suggests that physical processes concurring with the growth boundary layer may be responsible for the particle formation. In this study spatial scale of the particle formation observed in the downtown area is assessed using aircraft data. In a case where newly formed particles grew to the detectable size (~50nm) of a single particle mass spectrometer (also deployed at the building site), results from chemical composition observations will be presented.